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Solar, whats your angle?

A client requested a consultation recently. He was building an out of state vacation home and it was time for solar. He had several quotes in hand for fixed panel roof mounted PV systems that were confusing. It seems these days every one needs a gimmick to sell their solar systems. Special panels, racks, etc. abound. One installer wanted to use a dome type mount that faces one panel east and one west each tilted at 10 degrees. This would produce “substantially more power” was the claim. I knew this was not possible so I ran the data through the PVwatts caculator. The results where shocking with 18% loss of energy produced yearly compared to South facing panels mounted a the optimum angle of 38-39 degrees. Don’t get me wrong these racks have their place in industrial applications and where space is at a premium. Properly tilted racks will shade each other if spaced to closely. So well these racks can solve some problems, the cost per watt goes up. Since the goal is to keep the cost per watt down these rack are almost never appropriate for residential solar.

So how do we maximize our energy return on investment?

Every square foot of our planet has a solar potential. If you’ve invested in solar panels your mission is clear. You must maximize that potential. Even with the recent drop in prices solar panels are not cheap. That considerable investment will be hanging there making power for a long time. It makes sense to…… maximize that potential! A flat panel collector (solar panel) will produce the most power when it is perpendicular to the light source or the sun. The sun produces the most energy at its apex in the sky from our perspective. That in a nutshell determines your angle, or rather your angles. Azimuth or rotation is easy. Panels should always face true south if you are in the northern hemisphere. Elevation angle or optimum tilt is a little more complicated since it varies with the seasons and latitude. Every thing you need to know for seasonal tilting is available here and many other sites on the web. If your application does not allow for tilting you can find everything you need to know using the PVwatts calculator. Grid tied folks with fixed panels will want to optimize yearly harvest to offset their electric bill. Off grid folks may want to optimize for the winter months when the shorter days make energy harvest a challenge.

It’s not always possible to have our panels at the optimum tilt. Site variable will often require some compromise. Knowing that angle and being able to determine the losses when we deviate from that angle is the key to good decision making.